I am trying to set up a back up thermostat to my main thermostat. I am running a VE300 with a VE100 as backup.

I hooked everything up. Was told to plug the VE100 into the power source and then plug the VE 300 into the back of the VE100. But, when i turned on the power only the VE100 is the only one that came on

Can any one help me figure this out.